1. Field of the Invention
The present invention relates to an information burying apparatus and method for burying information in an image and further relates to a method of detecting buried information. In particular, the present invention develops a burying method for making buried information less conspicuous.
2. Description of the Related Art
By superimposing information other than an image on the image, it is possible to record secondary information concerning the image. As such secondary information, it is possible to bury information during image creation, for example, information concerning a printing date and time, a printing person, a printer, and the like. This makes it possible to prevent manipulation and counterfeiting of an image and an image print using this secondary information.
As a method of superimposing information on an image, a system described below is known in the past.
JP-A-2003-209676 discloses a system with which plural patterns having different spatial frequencies are prepared, a combination of these patterns is selected according to content of information to be buried, and the patterns are arranged on an image. When this image is scanned by a scanner, filtering for detecting the respective patterns is performed and a filter output of the image is compared with reference information. Consequently, it is possible to specify types of patterns in respective areas of the image. It is possible to reproduce the buried information by checking a combination and an arrangement of these patterns. In this system, plural dots are arrayed from a predetermined frequency in the respective patterns. Therefore, an overall pattern including a combination of these patterns is recognized as an aperiodic and irregular pattern and a feeling of noise in an image is caused.
JP-A-2003-2646868 discloses a method of burying information in an image by changing parameters of a dither method. Specifically, according to switching of threshold data of a dither matrix, a shape and a phase of a dither pattern changes according to buried information. This makes it unnecessary to apply substantial change or addition to a circuit in the past and makes it possible to easily perform burying of information. However, in this system, although it is possible to change a phase of a dither pattern, it is impossible to change the phase for each of dots. Therefore, reference information is necessary to detect a phase of a pattern. For that purpose, it is necessary to print reference information such as register and detect the reference information or detect an edge of paper. As a result, processing is complicated.